The present invention relates generally to field-assisted gas storage systems. More specifically, the present invention relates to field-assisted hybrid hydrogen storage system, wherein hydrogen and electrical energy are stored in the form of protons and electrons.
Hydrogen is considered to be an ideal fuel for fuel cell vehicles. Typically, hydrogen fuel cells operate by converting the chemical energy in hydrogen and oxygen into water, producing electricity and heat, which electricity is then fed into an electric motor that powers the wheels of a fuel cell vehicle.
Hydrogen is the most plentiful element in the universe, is the third most plentiful element on Earth, can be derived from multiple renewable energies, and, when consumed as fuel in a fuel cell, produces only water without the production of greenhouse gases such as carbon dioxide. Conventional means of storing hydrogen for end use delivery include: (1) liquid or gaseous hydrogen, (2) hydrocarbon fuels (i.e., fossil fuels), and (3) solid materials (i.e., metal hydrides).
Using liquid or gaseous hydrogen as the energy source in a fuel cell is not ideal. Hydrogen is highly flammable and requires a low hydrogen-to-air concentration for combustion. Furthermore, hydrogen is harder to transport and store than other liquid fuels. Additionally, there is currently only a very limited infrastructure available for distributing hydrogen to the public.
Hydrogen storage materials that chemically store the hydrogen fuel are considered to be an advantageous source of hydrogen for fuel cells and in a wide range of potential applications. However, getting sufficient hydrogen solubility, storage density, and mobility in such materials has proven to be difficult. Furthermore, the ability to control the rates of hydrogen uptake and release over a broad range of power output for applications such as fuel cells has not yet been achieved. Therefore, improved hydrogen storage materials are desired for a variety of applications, including selective hydrogen separation from other gases, catalysis, and fuel cells for vehicles, personal power generation, and stationary power generation.
Extensive research activity in the past 30 or so years has focused on storing hydrogen in the form of solid metal hydrides. Metal hydrides are typically generated exothermically when metals and alloys are exposed to hydrogen. Most of the hydrogen reacts with these metals or alloys and forms new compounds, while a smaller portion of the hydrogen decomposes into atomic hydrogen in the exothermic reaction and subsequently enters interstices in the metal lattice. The hydrogen can be recovered for use by heating, by electrolytic oxidation of the hydride, or by a reaction with an oxide or water. One advantage of using a metal hydride for hydrogen storage is that the volume density for hydrogen storage in metal hydrides is relatively large in comparison to other storage media. However, recovering the hydrogen from the hydride is difficult, as is regenerating the metal. Moreover, the metal adds significant weight to the fuel cell system.
Examples of well-known hydrogen storage materials include metal hydrides, such as FeTiH2 and LaNi5H6, which hydrides release hydrogen upon heating. Even though FeTiH2 and LaNi5H6 have acceptable recovery temperatures, the hydrogen content in terms of weight percent is too low for use in vehicular fuel cell applications. Other metal hydrides, such as MgH2 and TiH2, have higher hydrogen contents, about 7.6 and about 4.0 percent by weight respectively, but must be heated to high temperatures (i.e., above about 100° C.) in order to recover the hydrogen. Other drawbacks to the use of metal hydrides as gas storage materials include disproportionation, poisoning, accompanying losses of capacity, and the need for regeneration of some of the storage alloys.
Carbon nanotubes are another potential hydrogen storage material that have been studied extensively. Carbon nanotubes are fullerene-related structures that consist of seamless graphite cylinders closed at either end with caps containing pentagonal rings. Carbon nanotube powders tend to pack inefficiently and have poor volumetric efficiency. Furthermore, carbon nanotubes are very expensive to produce, and currently are not available in the quantities that are needed for commercial hydrogen storage applications.
The future hydrogen economy requires efficient ways to store and transport hydrogen for automobile and distributed power fuel cell applications, and numerous other applications. Several methods have been proposed for hydrogen storage, including those discussed above, but currently, none of the materials or methods has demonstrated the desired hydrogen storage density, hydrogen mobility, and/or hydrogen uptake/release capability needed for commercial applications.
Therefore, it would be desirable to have gas storage materials that are light, compact, relatively inexpensive, safe, and easy to use. It would be further desirable to have gas storage materials that provide capability of storing and releasing hydrogen at atmospheric temperature and pressure. It would also be desirable to have such materials comprise a mechanism that allows the charging/uptake and releasing of gas to be well controlled.